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<FONT color="green">001</FONT>    package gates;<a name="line.1"></a>
<FONT color="green">002</FONT>    <a name="line.2"></a>
<FONT color="green">003</FONT>    import register.Register;<a name="line.3"></a>
<FONT color="green">004</FONT>    import gates.FunctionGate;<a name="line.4"></a>
<FONT color="green">005</FONT>    import mathtools.Complex;<a name="line.5"></a>
<FONT color="green">006</FONT>    import java.util.Random;<a name="line.6"></a>
<FONT color="green">007</FONT>    <a name="line.7"></a>
<FONT color="green">008</FONT>    /**<a name="line.8"></a>
<FONT color="green">009</FONT>     * The measurement gate which measures the state of all the qubits in the register simultaneously.<a name="line.9"></a>
<FONT color="green">010</FONT>     * It collapses the wavefunction and is an irreversible gate. <a name="line.10"></a>
<FONT color="green">011</FONT>     * @author Jan Zaucha<a name="line.11"></a>
<FONT color="green">012</FONT>     *<a name="line.12"></a>
<FONT color="green">013</FONT>     */<a name="line.13"></a>
<FONT color="green">014</FONT>    public class Measurement extends FunctionGate {<a name="line.14"></a>
<FONT color="green">015</FONT>    <a name="line.15"></a>
<FONT color="green">016</FONT>            /** Create a random number generator. <a name="line.16"></a>
<FONT color="green">017</FONT>             * Need to store as we can seed the RNG<a name="line.17"></a>
<FONT color="green">018</FONT>             */<a name="line.18"></a>
<FONT color="green">019</FONT>            private Random randomGenerator;<a name="line.19"></a>
<FONT color="green">020</FONT>    <a name="line.20"></a>
<FONT color="green">021</FONT>            /**<a name="line.21"></a>
<FONT color="green">022</FONT>             * Constructor (no specified seed)<a name="line.22"></a>
<FONT color="green">023</FONT>             */<a name="line.23"></a>
<FONT color="green">024</FONT>            protected Measurement(){<a name="line.24"></a>
<FONT color="green">025</FONT>                    randomGenerator = new Random();<a name="line.25"></a>
<FONT color="green">026</FONT>            }<a name="line.26"></a>
<FONT color="green">027</FONT>            <a name="line.27"></a>
<FONT color="green">028</FONT>            /**<a name="line.28"></a>
<FONT color="green">029</FONT>             * Constructor (specified seed)<a name="line.29"></a>
<FONT color="green">030</FONT>             * <a name="line.30"></a>
<FONT color="green">031</FONT>             * @param seed<a name="line.31"></a>
<FONT color="green">032</FONT>             */<a name="line.32"></a>
<FONT color="green">033</FONT>            public Measurement(long seed){<a name="line.33"></a>
<FONT color="green">034</FONT>                    randomGenerator = new Random(seed);<a name="line.34"></a>
<FONT color="green">035</FONT>            }<a name="line.35"></a>
<FONT color="green">036</FONT>            <a name="line.36"></a>
<FONT color="green">037</FONT>            /**<a name="line.37"></a>
<FONT color="green">038</FONT>             * set the seed<a name="line.38"></a>
<FONT color="green">039</FONT>             * @param seed  <a name="line.39"></a>
<FONT color="green">040</FONT>             */<a name="line.40"></a>
<FONT color="green">041</FONT>            public void setSeed(long seed){<a name="line.41"></a>
<FONT color="green">042</FONT>                    randomGenerator.setSeed(seed);<a name="line.42"></a>
<FONT color="green">043</FONT>                    <a name="line.43"></a>
<FONT color="green">044</FONT>            }<a name="line.44"></a>
<FONT color="green">045</FONT>    <a name="line.45"></a>
<FONT color="green">046</FONT>            /**<a name="line.46"></a>
<FONT color="green">047</FONT>             * Returns the name of the gate regardless of representation.<a name="line.47"></a>
<FONT color="green">048</FONT>             */<a name="line.48"></a>
<FONT color="green">049</FONT>            public String getName() {<a name="line.49"></a>
<FONT color="green">050</FONT>                    return "Measurement";<a name="line.50"></a>
<FONT color="green">051</FONT>            }<a name="line.51"></a>
<FONT color="green">052</FONT>    <a name="line.52"></a>
<FONT color="green">053</FONT>            /**<a name="line.53"></a>
<FONT color="green">054</FONT>             * Measures the state of all the qubits simultaneously.<a name="line.54"></a>
<FONT color="green">055</FONT>             * note: this is an irreversible gate,<a name="line.55"></a>
<FONT color="green">056</FONT>             * the measurement collapses the wavefunction<a name="line.56"></a>
<FONT color="green">057</FONT>             * See interface &lt;code&gt;Gate&lt;/code&gt; for usage.<a name="line.57"></a>
<FONT color="green">058</FONT>             * @param r the register <a name="line.58"></a>
<FONT color="green">059</FONT>             */<a name="line.59"></a>
<FONT color="green">060</FONT>            public void apply(Register r) {<a name="line.60"></a>
<FONT color="green">061</FONT>                    <a name="line.61"></a>
<FONT color="green">062</FONT>                    // prepare the array for the new register<a name="line.62"></a>
<FONT color="green">063</FONT>                    Complex [] newRegister = new Complex [r.getHeight()]; <a name="line.63"></a>
<FONT color="green">064</FONT>                    for(int j=0; j&lt;r.getHeight(); j++){<a name="line.64"></a>
<FONT color="green">065</FONT>                            newRegister[j] = new Complex(0.0);<a name="line.65"></a>
<FONT color="green">066</FONT>                    }<a name="line.66"></a>
<FONT color="green">067</FONT>                    // first draw a random number between 0 (inclusive) and 1<a name="line.67"></a>
<FONT color="green">068</FONT>                    double random = Math.random();<a name="line.68"></a>
<FONT color="green">069</FONT>                    //check which state is the register in<a name="line.69"></a>
<FONT color="green">070</FONT>                    double currentPosition = 0.0; // this is the "position" along a normalized probability line <a name="line.70"></a>
<FONT color="green">071</FONT>                    for(int i=0; i&lt;r.getHeight(); i++){<a name="line.71"></a>
<FONT color="green">072</FONT>                            currentPosition += r.getElement(0, i).getMagnitudeSquared();<a name="line.72"></a>
<FONT color="green">073</FONT>                            if(random &lt; currentPosition){<a name="line.73"></a>
<FONT color="green">074</FONT>                                    // collapse the wavefunction<a name="line.74"></a>
<FONT color="green">075</FONT>                                    newRegister[i]= new Complex(1.0);<a name="line.75"></a>
<FONT color="green">076</FONT>                                    r.update(newRegister);<a name="line.76"></a>
<FONT color="green">077</FONT>                                    break;  // break loop so that register stays in this state<a name="line.77"></a>
<FONT color="green">078</FONT>                            }<a name="line.78"></a>
<FONT color="green">079</FONT>                    }<a name="line.79"></a>
<FONT color="green">080</FONT>    <a name="line.80"></a>
<FONT color="green">081</FONT>    <a name="line.81"></a>
<FONT color="green">082</FONT>            }<a name="line.82"></a>
<FONT color="green">083</FONT>    <a name="line.83"></a>
<FONT color="green">084</FONT>    <a name="line.84"></a>
<FONT color="green">085</FONT>    <a name="line.85"></a>
<FONT color="green">086</FONT>    }<a name="line.86"></a>




























































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